1. Field of the Invention
The present invention relates to a method of deforming a microcellular polyurethane component which can be utilized as a coil spring isolator or a jounce bumper.
2. Description of the Related Art
Methods of forming components from microcellular polyurethane (MCU) are known in the art. A component made of MCU is formed by mixing and injecting a liquid reaction mixture into a reaction mold. The liquid reaction mixture reacts and solidifies such that the component is in a partially cured state, i.e. a gelled state. In the partially cured state, the MCU has the physical property of being solid and the chemical bonds of the MCU are not completely formed. The component is then heated to cure the MCU, i.e. to complete the formation of the chemical bonds. The curing of the MCU makes the component more durable.
When the liquid reaction mixture reacts and solidifies, the component is formed in the shape of the reaction mold. The reaction mold is sized and shaped such that the component is formed in a desired size and shape. Difficulties arise with the current methods of forming MCU components when the component is thin, specifically when the component is less than 8 mm thick. Difficulties also arise when the component has a complex shape, such as sharp angles. Specifically, the reaction mixture is viscous and does not easily flow into and fill thin and complexly shaped reaction molds.
When the liquid reaction mixture reacts and solidifies, the component has a uniform density. Backings or skeletons having a density greater than or less than the density of the MCU are attached to the MCU such that the component has varying density. However, current methods of forming components from MCU are not conducive to forming one-piece components of common homogeneous MCU having varying density.
It is known in the prior art to thermoform components of certain materials to increase the density of the component and to shape the component. Specifically, components made of thermoplastic material are more conducive to thermoforming in comparison to components made of thermosetting material. Thermoplastic material is defined by molecules that do not chemically bond with each other when heated. Consequently, thermoplastic material can be repeatedly softened by heating and hardened by cooling. Thermoplastic materials melt without degrading because the melt temperature is lower than the chemical degradation temperature. In contrast, thermosetting material is defined by molecules that chemically bond with each other when heated. Thermosetting materials cannot melt without degrading because the melt temperature is higher than the chemical degradation temperature. Molecules of thermosetting material cross-link with each other to create a permanent three-dimensional molecular network.
Thermoforming includes the steps of heating the component and compressing the component such that the component is shaped and is increased in density. For example, U.S. Pat. No. 6,368,702 to Erickson (the '702 patent) discloses a method of thermoforming a component formed from thermoplastic material. The '702 patent discloses heating a thermoplastic foam sheet and compressing the thermoplastic foam sheet to deform the component to define a thin, highly compressed portion and a thick, non-compressed portion. The '702 patent does not disclose a method of deforming a component formed of thermosetting material, such as MCU, to shape the component and to increase the density of a first portion of the component relative to a second portion of the component.
Accordingly, it would be desirable to identify a method of deforming a component formed of materials other than thermoplastic materials into thin and/or complex shapes. Additionally, it is desirable to identify a method of deforming a component formed of materials other than thermoplastic materials such that the component has varying density.